AD9731 查看數據表（PDF） - Analog Devices

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AD9731

10-Bit, 170 MSPS D/A Converter

Analog Devices 

AD9731

The REFERENCE IN pin can also be driven directly for wider

bandwidth multiplying operation. The analog signal for this mode

of operation must have a signal swing in the range of –3.3 V to

–4.25 V. This can be implemented by capacitively coupling into

REFERENCE IN a signal with a dc bias of –3.3 V (IOUT ª

22.5 mA) to –4.25 V (IOUT ª 3 mA), as shown in Figure 4, or by

dividing REFERENCE IN with a low impedance op amp whose

signal swing is limited to the stated range.

NOTE: When using an external reference, the external refer-

ence voltage must be applied prior to applying –VS.

APPROX

–3.8V

AD9731

REFERENCE IN

–VS

–VS

An operational amplifier can also be used to perform the I-to-V

conversion of the DAC output. Figure 5 shows an example of a

circuit that uses the AD9631, a high speed, current feedback

amplifier. The resistor values in Figure 5 provide a 4.096 V

swing, centered at ground, at the output of the AD9631 amplifier.

10k⍀

1/2

AD708

10k⍀

1/2

AD708

R1

200⍀

IFS

R2

100⍀

REF CONTROL

OUT AMP IN

IOUT

AD9731

RFF

IFS 25⍀

RL

25⍀

RFB

400⍀

AD9631

2048V

VOUT

IOUTB

25⍀

Figure 4. Wideband Multiplying Circuit

Analog Output

The switch network provides complementary current outputs

IOUT and IOUTB. The design of the AD9731 is based on statisti-

cal current source matching, which provides a 10-bit linearity

without trim. Current is steered to either IOUT or IOUTB in pro-

portion to the digital input word. The sum of the two currents is

always equal to the full-scale output current minus 1 LSB. The

current can be converted to a voltage by resistive loading as

shown in the block diagram. Both IOUT and IOUTB should be

equally loaded for best overall performance. The voltage that is

developed is the product of the output current and the value of

the load resistor.

Figure 5. I-to-V Conversion Using a Current Feedback

Amplifier

EVALUATION BOARD

The performance characteristics of the AD9731 make it ideally

suited for direct digital synthesis (DDS) and other waveform

synthesis applications. The AD9731 evaluation board provides a

platform for analyzing performance under optimum layout con-

ditions. The AD9731 also provides a reference for high speed

circuit board layout techniques.

–10–

REV. B

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